The present invention relates to devices for injecting, infusing, administering, delivering or dispensing a substance, and to methods of making and using such devices. More particularly, it relates to an appliance for administering a fluid product, e.g. a medication in liquid form. This type of appliance may be referred to herein by the designation “administration appliance,” and it also may be thought of and/or referred to by using terms such as medical device, injection device, administration device, injection pen, infusion device, and the like.
Various diseases may make it necessary to administer a liquid medication to a patient over a prolonged period of time, e.g., an insulin preparation or a blood-thinning medication such as heparin. Compact, portable administration appliances are known for this purpose, which patients always carry with them, close to their bodies. The medication container in such administration appliances is most often a carpule, i.e., a glass container incorporating a sliding plug or piston. The carpule (also referred to often as an ampoule or ampule or vial) is connected with an infusion set, the syringe of which empties into the bodily tissue of the patient. A suitable drive or power source, e.g., a spring drive or an electric motor, advances the plug into the carpule, thereby ejecting the medication from the carpule. After a carpule has been emptied, it is removed from the administration appliance and replaced by a new carpule.
In many portable administration appliances, the plug is advanced in the carpule by a threaded rod, which acts as a piston rod on the plug. A rotatable nut secured against displacement runs on the threaded rod, and is driven by an electric motor. By a rotation of the nut, the threaded rod is advanced. Generally, the electric motor is situated next to the carpule to limit the length of the administration appliance, and simplify replacement of the carpule.
U.S. Pat. No. 6,248,093 discloses an administration appliance in which the drive motor and the transmission are arranged coaxially with the medication reservoir. The plug of the medication reservoir is advanced by a sleeve-like feed element, which is connected by an inner thread with a drive screw driven by the motor, and thereby linearly advanced. In its initial position, the feed element at least partially envelops the motor transmission. The feed element is part of the base unit, while the plug is part of the replaceable medication reservoir. Therefore, the feed element and plug can be detached from each other. To prevent unintentional ejection of the medication due to ambient pressure fluctuations, the feed element and the plug are connected in such a way that the connection can also absorb tensile forces during operation of the administration appliance. In this way, the plug is forced to follow the motion of the feed element, and pressure fluctuations cannot advance the plug further than prescribed by the position of the feed element. During replacement of the medication reservoir, the plug and the feed element are detached from each other in a rotational motion. The feed element is then returned to its initial position by the motor. On the one hand, this arrangement requires a relatively complicated connection between the plug and the feed element. On the other hand, it is necessary to return the feed element after the end of the administration. In addition, special measures must be taken for cases in which an incompletely filled medication reservoir is used.
Handling the carpules or medication containers or vials requires some dexterity, since they usually consist of glass, and are hence easily damaged. In addition, sterility is not always guaranteed while replacing the carpule. Therefore, administration appliances are also known in which the medication is present in a disposable cartridge, which is easier to insert into a base unit than is possible with a carpule, and contains other elements in addition to the medication container, which might come into contact with the medication, e.g., a luer lock connector for the infusion set. As a result, such a cartridge is more reliable and hygienic to use. As soon as the medication in the cartridge has been used, the latter is completely removed from the base unit, and a new cartridge is inserted into the base unit.